The global analysis of high-dimensional nonlinear floating raft system is researched by the method of Point Mapping Under Cell Reference(PMUCR) in the symmetrical excitation condition. The several necessary principles applied to high-dimensional systems are discussed. The impacts from the PMUCR parameters, including the length of calculation time, criterion of persistence of system characteristics and the step of mapping, on computing efficiency are analyzed by calculation method. The calculation result shows that the period motion is complex and the P-1 and P-2 motion is discovered in the plane. Finally, the stability of periodic motion is researched by the shooting method.